class Solution {
public:
    int uniquePaths(int m, int n) {
        vector<vector<int>> dp(m+1, vector<int>(n+1, 0));
        dp[1][1] = 1;
        for (int i = 1; i <= m; ++i) {
            for (int j = 1; j <= n; ++j) {
                if (dp[i-1][j] != 0) dp[i][j] += dp[i-1][j];
                if (dp[i][j-1] != 0) dp[i][j] += dp[i][j-1];
            }
        }
        return dp[m][n]; 
    }
};